1. Field of the Invention
The present invention relates to a tool holder which is used to attach a cutting tool, such as a burnishing reamer or a drill, to a main spindle of a machine tool, and which can correct run-out of the tip of the cutting tool.
2. Description of the Related Art
In machining performed by a machine tool, a cutting tool must be attached to a main spindle of the machine tool with high accuracy in order to enable accurate machining.
In general, in the case where a cutting tool is chucked by use of a tool holder, run-out of the cutting tool as measured at a point located away from the chucked portion of the cutting tool toward the tip thereof by a predetermined distance is used as an index that represents run-out accuracy. Even a precision tool holder has a run-out accuracy of 3 to 5 μm. In other words, even when a precision chuck is used for a tool holder of a burnishing reamer, drill, or the like, difficulty is encountered in reducing run-out of the tip of the tool to zero. Therefore, a tool holder capable of correcting run-out of the tip of a tool has been proposed and put to practical use.
Conventional tool holders equipped with a tip run-out correcting mechanism will be described with reference to FIGS. 1 and 2.
FIG. 1 is a partially sectioned side view of a conventional tool holder equipped with a tip run-out correcting mechanism.
As shown in FIG. 1, a tool holder 1 includes a taper shank portion 2 to be attached to a main spindle of an unillustrated machine tool; a flange 3, which is formed at a larger-diameter-side end of the shank portion 2 and used for gripping the tool holder 1; and an arbor 4, which is formed integrally with the flange 3 in such a manner that the arbor 4 extends from an end of the flange 3 opposite the shank portion 2, and its axis is aligned with that of the flange 3. A cutting tool 6 such as a drill is attached to a tip portion of the arbor 4 by means of a collet chuck 5.
A shoulder portion 4a having a diameter greater than that of the arbor 4 is formed at a boundary between the arbor 4 and the flange 3. A rotary ring 7, which constitutes a tip run-out correcting mechanism, is rotatably fitted onto the shoulder portion 4a. A fixation bolt 8 radially penetrates the rotary ring 7 at an axial position facing the shoulder portion 4a and is in screw-engagement with the rotary ring 7. Thus, the rotary ring 7 can be fixed to the shoulder portion 4a by means of the fixation bolt 8. Further, four tip run-out correcting screws 9 radially penetrate the rotary ring 7 at an axial position facing a root portion of the arbor 4 and are in screw-engagement with the rotary ring 7.
When such a tool holder 1 is used, tip run-out of the cutting tool 6 is corrected as follows. An operator attaches to a main spindle of a machine tool the shank portion 2 of the tool holder 1, which carries the cutting tool 6. Subsequently, the operator brings a test indicator 10 into contact with a circumferential surface of a tip portion of the cutting tool 6. The operator measures the difference between the maximum and minimum readings of the test indicator 10 during rotation of the main spindle, as tip run-out of the cutting tool 6. Further, from the measured value, the operator determines an angular position at which the tip run-out of the cutting tool 6 becomes greatest. Subsequently, after rotation of the main spindle is stopped, the operator rotates the rotary ring 7 in such a manner that one of the correction screws 9 faces a circumferential surface section of the root portion of the arbor 4, the surface section corresponding to the angular position at which the tip run-out of the cutting tool 6 becomes greatest. The operator then fixes the rotary ring 7 by means of the fixation bolt 8. Subsequently, while viewing the test indicator 10, the operator tightens the correction screw 9 that faces the circumferential surface section of the root portion of the arbor 4 corresponding to the angular position at which the tip run-out becomes greatest, in order to elastically deform the arbor 4 in the screwing direction of the correction screw 9, to thereby correct the eccentricity of the tip of the cutting tool 6 in such a manner that the tip run-out of the cutting tool 6 approaches zero to a possible extent. Thus, the tip run-out of the cutting tool 6 can be corrected.
FIG. 2 is a partially sectioned side view of another conventional tool holder equipped with a tip run-out correcting mechanism.
As shown in FIG. 2, a tool holder 12 includes a taper shank 13 to be attached to a main spindle of an unillustrated machine tool; a flange 14, which is formed at a larger-diameter-side end of the shank 13 and used for gripping the tool holder 12; and an arbor 15, which is formed integrally with the flange 14 in such a manner that the arbor 15 extends from an end of the flange 14 opposite the shank portion 13, and its axis is aligned with that of the flange 14. A cutting tool 17 such as a drill is attached to a tip portion of the arbor 15 by means of a collet chuck 16.
In FIG. 2, reference numeral 18 denotes a run-out corrector for correcting tip run-out of the cutting tool 17 held on the tool holder 12 via the collet chuck 16. The run-out corrector 18 includes a ring member 181 and a push screw 182. The ring member 181 is removably attached to a tip portion of the arbor 15 and the periphery of a lock nut 161 of the collet chuck 16. The push screw 182 radially penetrates the ring member 181 and is in screw-engagement with the ring member 181.
When such a tool holder 12 is used, tip run-out of the cutting tool 17 is corrected as follows. An operator attaches to a main spindle of a machine tool the shank portion 13 of the tool holder 12, which carries the cutting tool 17. Subsequently, the operator brings a test indicator 19 into contact with a circumferential surface of a tip portion of the cutting tool 17. The operator measures the difference between the maximum and minimum readings of the test indicator 19 during rotation of the main spindle, as tip run-out of the cutting tool 17. Further, from measured value, the operator determines an angular position at which the tip run-out of the cutting tool 17 becomes greatest. Subsequently, after rotation of the main spindle is stopped, the operator rotates the ring member 181 in such a manner that the push screw 182 faces a peripheral portion of the lock nut 161, the portion corresponding to the angular position at which the tip run-out of the cutting tool 17 becomes greatest. Subsequently, while viewing the test indicator 19, the operator tightens the push screw 182 in order to apply pressure to that peripheral portion in the direction indicated by an arrow, to thereby correct the eccentricity of the tip of the cutting tool 17 in such a manner that the tip run-out of the cutting tool 17 approaches zero to a possible extent. Thus, the tip run-out of the cutting tool 17 can be corrected. After completion of run-out correction, the operator removes the run-out corrector 18 from the tool holder 12.
However, in the case of the tool holder 1 shown in FIG. 1, when the eccentricity of the tip of a tool is to be corrected, an operator must elastically deform the arbor 4 in a radial direction by radially pushing the root portion of the arbor 4 by use of the corresponding correction screw 9 of the tip run-out correction mechanism. Therefore, correction of tip run-out requires a large force. Therefore, such a conventional tip run-out correction mechanism can be applied only to tool holders for tools of small diameters.
Further, in the case of the tool holder 12 shown in FIG. 2, since the run-out corrector 18 is removed from the tool holder 12, after being corrected the tip of a-tool may return to the original eccentric or deviated position; i.e., the corrected position of the tip of the tool cannot be maintained stably.